Lua Enum

When start scripting with Lua one may notice that its functional range is some what reduced to a tiny set of essential basics. One thing I was missing at least is an enum type. But we could implement something very close.

Before we start I want to recommend the online demo at lua.org. Just paste your lua code into the lua-shell window and press “run” to see if it works.

A very simple enum function could be something like this:

-- Function enum
function enum (list)
  assert ("table" == type(list), "list have to be a table value.");
  local result = {}
  for i=1, #list do
    local name = list[i]
    assert ("string" == type(name), "enums have to be string values.");
    result[name] = i
    result[i] = name
  end
  return result;
end

With such a function you could use it quite similar to how you would use enums. Here is an example of an enum “InputDeviceType” that has three different enums: “Keyboard”, “Joystick” and “Mouse”. To get the value of the enum you simply use the initial storage “InputDeviceType” and use the enum storage as index.

Here is the example code:

-- typedef some enums:
local InputDeviceType = enum 
{ 
  "Keyboard", 
  "Joystick", 
  "Mouse" 
}

-- create a local value storing the enum number.
local myDevice = InputDeviceType.Keyboard;

-- here is an example of how you could get the enum name agin.
print( "Number:", myDevice, " Name:", InputDeviceType[myDevice] );
-- output
-- Number:1 Name: Keyboard

There is one drawback to this enum implementation, though. All enums have to be table type (array).